This invention relates to a process for eliminating 1-carboxy-1-phosphonocyclopentan-3-one (hereinafter referred to as "ketone") from, or reducing its content in, technical 2-phosphonobutane-1,2,4-tricarboxylic acid (hereinafter referred to as "PBTC") dissolved in water using bleaching liquor.
The industrial production of the corrosion and scale inhibitor, PBTC, is carried out in three steps. First, dimethyl phosphite is reacted with maleic anhydride to form phosphonosuccinic acid tetramethyl ester which is then converted into 2-phosphonobutane-1,2,4-tricarboxylic acid pentamethyl ester by reaction with methyl acrylate in the presence of sodium methylate as catalyst (DE-OS 2 061 838). The ester is then saponified to PBTC. In this process for the production of PBTC or rather an aqueous solution of PBTC, 1-phosphono-1-carboxycyclopentan-3-one is formed as secondary product, having an adverse effect in certain industrial applications of PBTC or rather aqueous solutions of PBTC or its Na, K or NH.sub.4 salts. For example, where PBTC is used in the production of special cleaning preparations, the aqueous solution darkens in color.
Accordingly, the problem addressed by the present invention was to provide a process which would enable this troublesome ketone to be eliminated from the aqueous solution of PBTC, or its content therein to be reduced, without destruction of the active substance PBTC.